Block copolymer-comprising compositions and methods of purifying PS-b-PXVP

ABSTRACT

In one embodiment, a block copolymer-containing composition includes PS-b-PXVP and a lithium salt, where “X” is 2 or 4. All lithium salt is present in the composition at no greater than 1 ppm by weight. In one embodiment, a homogenous block copolymer-including comprising has PS-b-PXVP present in the composition at no less than 99.99998% by weight, where “X” is 2 or 4. Methods of forming such compositions are disclosed.

TECHNICAL FIELD

Embodiments disclosed herein pertain to block copolymer-comprisingcompositions and to methods of purifying PS-b-PXVP from a solidcomprising PS-b-PXVP and a lithium salt, and from a solution comprisingdissolved PS-b-PXVP and a dissolved lithium salt.

BACKGROUND

Numerous applications exist in which it is desired to form repeatingpatterns having a small pitch (for example, a pitch of less than about50 nanometers). For instance, integrated circuitry fabrication mayinvolve formation of repeating patterns of memory storage units (i.e.,NAND unit cells, dynamic random access [DRAM] unit cells, cross-pointmemory unit cells, etc.). Additionally, nanoscale mechanical, chemical,biological and other electrical devices and systems are beingfabricated.

Photolithography is a conventional method used for fabrication ofnanoscale devices and systems. Photolithography uses incident radiationof a selected wavelength to pattern a photosensitive material. Theexposed or un-exposed portions of the photosensitive material are thenselectively removed relative to the other. The material which remains isused as a mask in patterning underlying substrate material which isexposed through openings in the mask.

A continuing goal in integrated circuitry fabrication is to increasecircuit density, and accordingly to decrease size of individualintegrated circuit components. Thus, there is a continuing goal to formpatterned masks to have increasing densities of individual features andless space between adjacent features. If photolithography alone is usedto pattern integrated circuit components, circuit density is limited bya threshold dictated by the minimal attainable feature size using theparticular photolithographic technology. The minimum feature size isdictated by, for example, a wavelength utilized during patterning of thephotosensitive material. Conventional photolithographic processingmethods are not readily capable of accommodating fabrication ofstructures and features much below the 100 nanometer level.

Methods have been developed which can be used in combination withphotolithography or other processing to push the minimum attainablefeature size to smaller dimensions than may be achieved withphotolithography alone. One such method is a procedure comprising use ofa block copolymer material to form a pattern between a pair ofphotolithographically-patterned, or other patterned, features. Blockcopolymer materials spontaneously assemble into periodic structures bymicrophase separation of the constituent polymer blocks upon annealingat a suitably high temperature. Such form ordered domains atnanometer-scale dimensions between the photolithographically-patterned,or other patterned, features. Following such self-assembly, one block ofthe copolymer can be selectively removed thereby leaving a mask havingnano-sized features and openings through which underlying substratematerial can be processed.

Copolymers are polymers derived from two or more monomeric species.Block copolymers contain two or more homopolymer subunits linked bycovalent bonds. Two example block copolymer materials arepolystyrene-b-poly2-vinylpyridine and polystyrene-b-poly4-vinylpyridine,and which are referred to herein as PS-b-PXVP where “X” is 2 or 4.

Conventional processes by which PS-b-PXVP is manufactured result inimpurities being received in the composition. Example impurities includelithium salts, for example lithium chloride. Some commercially availablePS-b-PXVP has lithium salt on the order of 400 to 500 parts per millionby weight in the composition. Such can result in lithium salt particleson the substrate on which the mask is being formed, and about whichblock copolymer patterns can form upon anneal as opposed to solelyrelative to the previously patterned features.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The invention in one embodiment comprises a block copolymer-comprisingcomposition which includes PS-b-PXVP and a lithium salt, where “X” is 2or 4, and wherein all lithium salt present in the composition totals nogreater than 1 ppm by weight. In one embodiment, all lithium salt ispresent in the composition at no greater than 0.1 ppm by weight. One ormore lithium salts may be present, with one example being lithiumchloride and a lower concentration of which was motivated by theproblems identified in the “Background” section above.

Salts other than lithium salt may also be present. If so, in oneembodiment, such other salts are individually present in the compositionat no greater then 10 ppm by weight. In one embodiment, any salts otherthan lithium salt are collectively present in the composition at nogreater than 25 ppm by weight. The composition may also include materialother than salt, for example, nickel, copper, and/or zinc. Thecomposition may or may not be homogenous. In one embodiment, thePS-b-PXVP is present in the composition at no less than 99.99998% byweight. Minimizing lithium salt content to no greater than 1 ppm byweight, and even more ideally to be no greater than 0.1 ppm by weight,may overcome the prior art problems identified above when used in blockcopolymer self-assembly in forming mask or other patterns on asubstrate. Heretofore, lowest known concentration of lithium salt in acomposition comprising PS-b-PXVP and a lithium salt is 50 ppm by weight.The composition may comprise one or both of PS-b-P2VP and PS-b-P4VP.

One embodiment of the invention is a homogenous blockcopolymer-comprising composition having PS-b-PXVP present in thecomposition at no less than 99.99998% by weight, and independent of anypresence of a lithium salt. Such composition may comprise one or both ofPS-b-P2VP and PS-b-P4VP. Prior art PS-b-PXVP-comprising compositionshave heretofore not included such above example purities, andaccordingly methods for producing such have not heretofore beendiscovered or developed.

Embodiments of the invention also include methods of purifying PS-b-PXVPfrom a solid comprising PS-b-PXVP and a lithium salt. The solid maycomprise one or both of PS-b-P2VP and PS-b-P4VP. In such embodiments,the solid comprising the PS-b-PXVP and lithium salt is dissolved in acarbon-containing liquid solvent, with such solvent itself being solublein liquid water. Examples include tetrahydrofuran, nitroethane,nitrobenzene, dimethlyformamide, acetone, methylethylketone, a pyridine,and a dioxane. Additionally, the carbon-containing liquid solvent mightinclude any combination of two or more of such example liquid solvents.Such act of dissolving can occur by any existing or yet-to-be developedmethod, and may be conducted at any suitable temperature and pressure,with ambient room temperature and pressure being an example. Further,embodiments of the invention include methods of purifying PS-b-PXVP froma solution comprising dissolved PS-b-PXVP, a dissolved lithium salt, anda carbon-containing liquid solvent that is soluble in liquid water. Thedissolved PS-b-PXVP may comprise one or both of PS-b-P2VP and PS-b-P4VP.

The carbon-containing liquid solvent having the dissolved PS-b-PXVP andlithium salt is combined with liquid water. An example ratio range ofliquid water to carbon-containing liquid solvent is from 2:1 to 1,000:1parts by volume, with 10:1 being a specific example. A first precipitateprecipitates out of the solution and has a greater concentrationPS-b-PXVP and less concentration lithium salt than was in the startingsolid. The combining of the carbon-containing liquid solvent having thedissolved solid with liquid water can occur at any suitable temperatureand pressure, with ambient room temperature and pressure being anexample. However, greater degree of precipitation may result attemperatures below room temperature. In one embodiment, thecarbon-containing liquid solvent having the dissolved solid and theliquid water are combined at a temperature no greater than 15° C., andin one embodiment at a temperature no greater than 10° C. Regardless, inone embodiment after combining the carbon-containing liquid solvent andwater and forming the first precipitate, the carbon-containing liquidsolvent may be boiled away from such combined solvent and liquid water.Such may result in additional of the first precipitate coming out ofsolution.

The first precipitate is dissolved in an organic liquid solvent that canform an azeotrope with water. Examples include dichloromethane,chloroform, tetrahydrofuran, benzene, carbon tetrachloride, toluene,ethylbenzene, ethylenedichloride, and 1,1,2-trichloroethylene. Further,the organic liquid solvent may include a combination of two or moreorganic liquid solvents. In one embodiment, the first precipitate iscollected by filtering or other manner to separate such from theremaining solution from which such was precipitated. The dissolving maybe conducted at any suitable temperature and pressure, with ambient roomtemperature and pressure being an example.

The organic liquid solvent having the dissolved first precipitate iscombined with liquid water. An aqueous liquid phase and an organicliquid phase are formed as a result of the combination. Such may occurat any suitable temperature and pressure, with ambient room temperatureand pressure being an example. Any suitable volume of water may beselected which results in formation of discernable aqueous and organicliquid phases.

The organic liquid phase is separated from the aqueous liquid phase.After such separating, liquid from the organic liquid phase is boiledaway and leaves a resultant precipitate. The first precipitate has morewater than any water in the resultant precipitate, and the resultantprecipitate has greater concentration of PS-b-PXVP and lessconcentration of lithium salt than was in the starting solid. In oneembodiment, the resultant precipitate has greater concentrationPS-b-PXVP than was in the first precipitate, and/or the resultantprecipitate has less concentration lithium salt than was in the firstprecipitate. Accordingly, the act of dissolving the first precipitate inan organic liquid solvent that can form an azeotrope with water,combining such with water, then separating out an organic liquid phasefollowed by boiling away the organic liquid phase may leave a morepurified solid in the form of a resultant precipitate. The resultantprecipitate may or may not have any remaining water. Regardless, suchact of forming of the resultant precipitate may also remove other salts,metals, or other materials thereby increasing the purity of thePS-b-PXVP.

The process may be repeated with respect to the resultant precipitate.For example, the resultant precipitate may be dissolved in an organicliquid solvent that can form an azeotrope with water, and which may ormay not be the same as the first-stated organic liquid solvent. Theorganic liquid solvent having the dissolved resultant precipitate wouldthen be combined with liquid water and another aqueous liquid phase andanother organic liquid phase formed therefrom. Such organic liquid phasewould be separated from the aqueous liquid phase, with liquid from suchorganic phase being boiled away to leave a product precipitate. Theresultant precipitate would have more water than any water that was inthe product precipitate, and the product precipitate would have greaterconcentration PS-b-PXVP and less concentration lithium salt than was inthe solid. Purity may also be improved in the product precipitaterelative to the resultant precipitate as identified above with theresultant precipitate relative to the first precipitate. Again, thewhole process could be repeated one or more additional times to achievegreater dryness and/or purity of PS-b-PXVP in the resultant and/orproduct precipitate.

In one embodiment, the resultant or product precipitate is ultimatelycollected. In one embodiment, the product precipitate may be collectedby dissolving it in another organic liquid solvent. Such may be of thesame composition as that as the organic liquid solvent that can form anazeotrope with water, or be of different composition. In one embodiment,such organic liquid solvent has a melting point greater than 0° C. and aboiling point less than 100° C. Examples include benzene, 1,4 dioxane,and nitrobenzene.

The organic solvent having the dissolved product precipitate therein isfrozen. Then, the organic liquid solvent is sublimated away to leave theproduct precipitate. Pressure and temperature can be selected by theartisan for the sublimation to avoid liquid formation.

EXAMPLE

A solid that was 0.58 grams of commercially available PS-b-P2VP (32.5kg/mole polystyrene and 12 kg/mole P2VP) was dissolved in 60 millilitersof tetrahydrofuran. The PS-b-P2VP prior to dissolving had approximately460 ppm of LiCl_(x), 23 ppm Na, 1 ppm K, 0.6 ppm Al, 0.4 ppm Ca, and 0.3ppm Zn, all by weight. The solid was added to the 60 milliliters oftetrahydrofuran, and stirred at ambient room temperature and roompressure until dissolved.

The resultant solution was poured into 500 milliliters of deionizedwater received within a 1,000 milliliter round bottom flask, causing awhite precipitate to form and collect in the bottom of the flask. Theflask was connected to a distillation apparatus, and the mixture washeated to approximately 50° C. and placed under 30 Torr vacuum causingthe liquid to boil. Such was continued for about two hours believed tobe effective to distill away substantially all of the tetrahydrofuran.The resulting mixture of water and white precipitate was allowed tosettle at ambient room temperature and pressure for 60+ hours.

The mixture was separated by pouring through a fritted glass funnel, andthe water discarded. The remaining solid white precipitate was dissolvedinto 100 milliliters of liquid dichloromethane. The liquiddichloromethane having the dissolved precipitate was combined withliquid water in a separatory funnel and rocked back and forth for about5 minutes, and then allowed to settle thereby forming resultant distinctaqueous liquid and organic liquid phases. Ten milliliters of water wasused, and the organic liquid phase and the aqueous liquid phase wereseparated by draining the organic liquid phase from the bottom of thefunnel flask. The water was discarded and the process repeated.

The resulting solution having dissolved precipitate therein wasdistilled at 39° C. for about 2 hours, with such being effective to boilaway the liquid dichloromethane and leave a solid precipitate adheringto sidewalls of the vessel. This process was repeated.

The resultant residual/product material was dissolved in 60 millilitersof benzene at a temperature of about 80° C., and the resulting solutionplaced in a sublimation vessel. The sublimation vessel was placed withina freezer at a temperature of about 0° C. for about two hours effectiveto freeze the solution having the dissolved residual precipitatetherein.

The sublimation vessel was then transferred to an ice bath, and thecontents of the vessel pumped down to 1 Torr effective to sublimate thebenzene away. The sublimation vessel was removed from the ice bath, andkept under vacuum pressure at room temperature overnight. Such left aproduct PS-b-P2VP precipitate of 0.522 grams. Such was PS-b-P2VPcontaining 0.1 ppm lithium chloride, 10 ppm Na, and all others at lessthan 10 ppm.

In compliance with the statute, the subject matter disclosed herein hasbeen described in language more or less specific as to structural andmethodical features. It is to be understood, however, that the claimsare not limited to the specific features shown and described, since themeans herein disclosed comprise example embodiments. The claims are thusto be afforded full scope as literally worded, and to be appropriatelyinterpreted in accordance with the doctrine of equivalents.

1. A method of purifying PS-b-PXVP from a solution comprising dissolvedPS-b-PXVP and a dissolved lithium salt, where “X” is 2 or 4, comprising:providing a solution comprising dissolved PS-b-P2VP, dissolvedPS-b-P4VP, and a dissolved lithium salt, the solution comprising acarbon-containing liquid solvent, the carbon-containing liquid solventbeing soluble in liquid water; combining the carbon-containing liquidsolvent having the dissolved PS-b-P2VP, dissolved PS-b-P4VP, and adissolved lithium salt with liquid water and precipitating a firstprecipitate therefrom, the first precipitate having greaterconcentration PS-b-P2VP and PS-b-P4VP and lower concentration of lithiumthan was in the solution; dissolving the first precipitate in an organicliquid solvent that can form an azeotrope with water; combining theorganic liquid solvent having the dissolved first precipitate withliquid water and forming an aqueous liquid phase and an organic liquidphase therefrom; separating the organic liquid phase from the aqueousliquid phase; and after the separating, boiling away liquid from theorganic liquid phase to leave a resultant precipitate, the firstprecipitate having more water than any water in the resultantprecipitate, the resultant precipitate having greater concentrationPS-b-P2VP and PS-b-P4VP and lower concentration of lithium than was inthe solution.
 2. The method of claim 1 wherein said providing comprisesdissolving a solid comprising PS-b-P2VP, PS-b-P4VP, and a lithium saltin the carbon-containing liquid solvent, the first precipitate havinggreater concentration PS-b-P2VP and PS-b-P4VP and lower concentrationlithium salt than was in the solid, the resultant precipitate havinggreater concentration PS-b-P2VP and PS-b-P4VP and lower concentrationlithium salt than was in the solid.
 3. The method of claim 1 wherein theresultant precipitate has greater concentration PS-b-P2VP and PS-b-P4VPthan was in the first precipitate.
 4. The method of claim 1 wherein theresultant precipitate has lower concentration lithium than was in thefirst precipitate.
 5. The method of claim 1 comprising before dissolvingthe first precipitate, boiling away carbon-containing liquid solventfrom the combined carbon-containing liquid solvent and liquid water. 6.The method of claim 1 comprising collecting the resultant precipitate.7. The method of claim 6 wherein the collecting comprises: dissolvingthe resultant precipitate in another organic liquid solvent; freezingthe another organic liquid solvent having the dissolved resultantprecipitate therein; and after the freezing, sublimating the anotherorganic liquid solvent away to leave another resultant precipitate. 8.The method of claim 7 wherein the another organic liquid solvent has amelting point greater than 0° C. and a boiling point less than 100° C.9. The method of claim 8 wherein the another organic liquid solventcomprises at least one of benzene; 1,4 dioxane; and nitrobenzene. 10.The method of claim 7 wherein the another organic liquid solvent and theorganic liquid solvent that can form an azeotrope with water are ofdifferent compositions.
 11. The method of claim 7 wherein the anotherorganic liquid solvent and the organic liquid solvent that can form anazeotrope with water are the same in composition.
 12. The method ofclaim 1 wherein the carbon-containing liquid solvent comprises at leastone of tetrahydrofuran, nitroethane, nitrobenzene, dimethlyformamide,acetone, methylethylketone, a pyridine, and a dioxane.
 13. The method ofclaim 1 wherein the combined carbon-containing liquid solvent having thedissolved solid and liquid water has from 2:1 to 1,000:1 by volume partswater to carbon-containing liquid solvent.
 14. The method of claim 1wherein the carbon-containing liquid solvent having the dissolved solidand the liquid water are combined at a temperature no greater than 15°C.
 15. The method of claim 1 comprising dissolving the resultantprecipitate in an organic liquid solvent that can form an azeotrope withwater; combining the organic liquid solvent having the dissolvedresultant precipitate with liquid water and forming another aqueousliquid phase and another organic liquid phase therefrom; separating theanother organic liquid phase from the another aqueous liquid phase; andafter the separating of the another organic liquid phase from theanother aqueous liquid phase, boiling away liquid from the anotherorganic liquid phase to leave a product precipitate, the resultantprecipitate having more water than any water in the product precipitate,the product precipitate having greater concentration PS-b-P2VP andPS-b-P4VP and lower concentration of lithium than was in the solution.16. A method of purifying PS-b-P2VP and PS-b-P4VP from a solidcomprising PS-b-P2VP, PS-b-P4VP, and a lithium salt, comprising:dissolving the solid in liquid tetrahydrofuran; combining the liquidtetrahydrofuran having the dissolved solid with liquid water andprecipitating a first precipitate therefrom, the first precipitatehaving greater concentration PS-b-P2VP and PS-b-P4VP and lowerconcentration lithium salt than was in the solid; dissolving the firstprecipitate in liquid dichloromethane; combining the liquiddichloromethane having the dissolved first precipitate with liquid waterand forming an aqueous liquid phase and an organic liquid phasetherefrom; separating the organic liquid phase from the aqueous liquidphase; and after the separating, boiling away liquid dichloromethanefrom the organic liquid phase to leave a resultant precipitate, thefirst precipitate having more water than any water in the resultantprecipitate, the resultant precipitate having greater concentrationPS-b-P2VP and PS-b-P4VP and lower concentration lithium salt than was inthe solid.
 17. The method of claim 16 comprising before dissolving thefirst precipitate, boiling away liquid tetrahydrofuran from the combinedtetrahydrofuran and liquid water.
 18. The method of claim 1 wherein alllithium salt present in the resultant precipitate is at no greater than1 ppm by weight of the resultant precipitate.
 19. The method of claim 18wherein all lithium salt present in the resultant precipitate is at nogreater than 0.1 ppm by weight of the resultant precipitate.
 20. Themethod of claim 1 comprising salts other than lithium salt present inthe resultant precipitate, the other salts collectively being present inthe resultant precipitate at no greater than 25 ppm by weight.
 21. Themethod of claim 1 comprising salts other than lithium salt present inthe resultant precipitate, the other salts individually being present inthe resultant precipitate at no greater than 10 ppm by weight.